Image: Cloud Vortices Off Saint Helena Island


NASA's Terra satellite passed over the South Atlantic Ocean on November 15, 2012, allowing the Moderate Resolution Imaging Spectroradiometer instrument flying aboard to capture this true-color image of St. Helena Island and the band of wind-blown cloud vortices trailing towards the island's leeward side.

St. Helena Island is a tiny island lying approximately 1,860 kilometers (1,156 miles) west of Africa. Volcanic in origin, it has rugged topography with steep, sharp peaks and deep ravines. Wind, which can blow unimpeded for hundreds of miles across the ocean, strikes the face of the mountains, and is forced around the unyielding terrain. As it blows around the island, the air spins on the leeward side, much like a flowing river forms eddies on the downriver side of a piling. The spinning wind forms intricate and mathematically predictable patterns.

When clouds are in the sky, these beautiful patterns become visible from above. Credit: NASA/GSFC/Jeff Schmaltz/MODIS Land Rapid Response Team. Larger image

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